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Summary of Completed Projects

Map of Downtown Palo Alto Projects

Scaffolding was erected and the street frontage mansard roofs were removed. The tile roofs are actually made out of galvanized steel sheets over wood framing.

The two-wythe-thick back wall was removed above the second floor, since it was bowed out of plane as a result of the earthquake. This wall was later rebuilt as a reinforced masonry wall with a center grout cavity.

Excavations for new shear wall footings required interior shoring and removal of otherwise undamaged framing.

The original masonry walls were supported on unreinforced concrete footings, with a low compressive strength. New footings were added where needed to support shear walls and old pipe columns, such as the one hanging down in the photo. Dowels were attached to tie existing footings to the new, deeper footings, wherever they came in contact. The shoring block seen in the photo is supported by a temporary spread footing below.

The new footing reinforcing cages were designed by current codes, with the lower layer of reinforcing steel passed under the original footings, and the upper layer of reinforcing passing through the old footings. The vertical bars will be part of the new concrete shear wall edge trimmer reinforcing.

At some locations, dowels were epoxy-set into the brick walls and tied into a reinforcing cage. Horizontal gaps were required where the new footing reinforcing laps the wall vertical steel, so that the new concrete wall could be properly sprayed-in-place using shotcrete.

A cast-in-place shear wall was added adjacent to the new elevator shaft, which was later tied to the second floor diaphragm. The temporary steel shoring was eventually removed.

The Sixth Street arches had opened up during the earthquake. While the original masonry was retained, an eight-inch thick layer of reinforced shotcrete was added on the interior surface, to provide vertical and lateral support.

Prior to adding the new shear walls, a footing was needed to support the outer edge shear walls, while also adding new support elements for the second story.

This interior shear wall is corbeled to support a drag tie that picks up the second floor lateral forces while providing increased vertical load capacity.

From the inside, bolts were epoxy-set into the exterior sandstone blocks, tested, and then dry-packed with mortar at the inner brick wythes. The bolts were then connected to an out-of-plane force-resisting element.

In order to avoid exterior and interior visual interruptions, out-of-plane forces were resisted by vertically drilling down the wall centerline, then installing a reinforcing bar and filling the hole with a polyester resin mixed with sand. This required removal of the mansard framing at some locations. This "center-coring" allowed preservation of the historic architectural fabric that would otherwise have to be removed.